To restrict the access to a particular IP address or network, specify --source option for the load balancer and firewall policy.

Note: When multiple (firewall or load balancer) rules are specified, make sure that the protocols, ports and sources are separated by a comma and in the same order. In a firewall policy create command, specify GRE, ICMP and IPSEC protocols last, for instance
--protocol TCP,TCP,UDP,TCP/UDP,GRE,ICMP,IPSEC.